1. Field of the Invention
The present invention relates to a technical field of a network-linked digital terrestrial television broadcasting system provided with both a digital television broadcast reception function and a bi-directional digital data communication function using a public telecommunication network where both the functions can operate in association with each other. In particular, the invention relates to a system and method of network-linked digital terrestrial television broadcasting in which an operation for data communication via a public telephone network is controlled on the basis of monitoring the result of a digital television broadcasting reception status.
2. Description of the Related Art
Since December 2003, Hivision program-based terrestrial digital broadcasting for household television sets has been operating in three major metropolitan districts of Japan: Tokyo, Nagoya, and Osaka. Its viewable area will gradually expand in years to come. Then in 2011, all the existing analog television broadcasting will stop, and the transition to the terrestrial digital broadcasting is expected to be completed.
Furthermore, preparation is under way for implementation of terrestrial digital broadcasting for mobile terminals such as cellular phones and personal digital assistances (PDA) (hereinafter, referred to as 1 segment broadcasting service) The 1 segment broadcasting service uses a low communication bit rate of 2 Mbps or lower and therefore can only transmit low-resolution video as compared with the terrestrial digital broadcasting for household television sets. However, the realization of a new service, which has been difficult, is now anticipated such as stable reception of the broadcast by devices in motion or the integration of the broadcast reception with data communication by making use of a mobile terminal's characteristics. Above all, a linked service system of the broadcast reception and the data communication can easily be structured by adding a reception function for the 1 segment broadcasting service to a cellular phone so the cellular phone industry is paying particular attention to the new service.
When the network-linked digital terrestrial television broadcasting function operates on the cellular phone, depending on a certain particular condition, a failure such as interruption of television broadcast reproduction may be caused because of an occurrence of a reception error in the 1 segment broadcasting service due to the influence of a transmission electric wave on a data communication side. To ensure an acceptable video reduction quality in the 1 segment broadcasting service, avoiding this problem is a very critical issue.
As a conventional art for solving this problem, for example, Japanese Laid-Open Patent Application No. 2003-009222 discloses a method of stopping a transmission operation based on the determination that a reception side will suffer a negative effect when a sum of an electric power of a transmission electric wave and an electric power of a reception electric wave exceeds a predetermined threshold.
Japanese Laid-Open Patent Application No. 2004-146910 also discloses a method of predicting a degradation condition of the reception sensitivity through a calculation from a relation between a transmission electric wave frequency and a reception electric wave frequency and changing the transmission frequency when it is judged that degradation of the sensitivity on the reception side will occur on the basis of the prediction.
However, according to the method disclosed in Japanese Laid-Open Patent Application No. 2003-009222, no mechanism is provided for confirming whether or not the reception side actually suffers a negative effect even when the sum of the electric power of the transmission electric wave and that of the reception electric wave exceeds the predetermined threshold so there is a problem in that accuracy of avoiding the reception failure cannot be secured. In addition, according to the method disclosed in Japanese Laid-Open Patent Application No. 2004-146910, although the degradation condition for sensitivity on the reception side is predicted through the calculation from the relation between the operating transmission electric wave frequency and the operating reception electric wave frequency, no mechanism is provided for confirming whether or not the reception side actually suffers a negative effect in this case too. Thus, there is also a problem in that the accuracy of avoiding the reception failure cannot be secured. Moreover, when both the functions of the reception of the 1 segment broadcasting service and the data communication are realized in a compact mobile terminal such as a cellular phone, an antenna for receiving the 1 segment broadcasting service and another antenna for performing the data communication need to be mounted physically close to each other. Thus, the influence of the transmission electric wave on the data communication side more severely disturbs the reception of the 1 segment broadcasting service.